Rotating machine with cooled hollow rotor bars

ABSTRACT

A rotating machine including a rotating shaft: a plurality of conductive rotor bars spaced from the rotating shaft and fixed to the rotating shaft through at least one intermediate member, where at least one of the plurality of conductive rotor bars have at least one first internal conduit; and a circulator for establishing a coolant circulation through the first internal conduit.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No. 09/598,731filed on Jun. 21, 2000 the disclosure of which is incorporated herein byits reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to rotating machines such aselectric motors and generators and, more particularly, to electricmotors and generators having a current-carrying stator with an inducedcurrent in a rotating inner rotor with coolant passing through thecurrent carrying portion of the rotor.

2. Prior Art

There have been many proposals intended to improve the operation oftransducers for electrical power/mechanical power conversion (motors orgenerators). However, there are still areas where the use of electricmotors remains impractical, for example for use as the main drive of avehicle such as a car. Current electric motors are generally too large,heavy, and produce too little power (especially at high speed) forcommercial use in a vehicle such as a car.

One problem associated with electrical machines, such as electricmotors, is that it is necessary to cool them because they generate heatwhich reduces their efficiency. The need for optimization in cooling iseven more important as increases in performance demands smallerpackages. At present such machines may be cooled by blowing air throughor over them. For heavy duty applications it is known to spray oil ontothe rotor and stator assemblies and into the gap between them using ahigh pressure pump. A scavenger pump may also be provided to collect thesprayed oil for re-cycling.

A common configuration for such motors is to have an inner rotor mountedon a straight shaft supported by bearings on the ends. The bearings aremounted in end covers that support and locate the rotor in the center ofa current-carrying stator. The rotor contains multiple current-carryingbars which run length wise parallel to the shaft and are located nearthe outer circumference of the rotor. Heat is produced in the rotor whenthe current in the stator excites the bars. Heat dissipation limits thedesign of the rotor. Another method used to dissipate heat is to passoil coolant through a hollow rotor shaft, referred to as back ironcooling. Heat generated in the rotor conductor bars is dissipated intothe core of the rotor, then into the rotor shaft and then into the oilcoolant flowing through the shaft and exits the rotating machine to aheat exchanger. Although this cooling method has its advantages, such assimplicity in design, it is desirable to increase the amount of heatconduction away from the rotor bars of the motor and to concentrate thecooling at the source of the heat, namely, the rotor bars.

SUMMARY OF THE INVENTION

Therefore it is an object of the present invention to provide a rotatingmachine with cooled hollow rotor bars which provides an increased amountof cooling than is provided by prior art methods for cooling rotatingmachines.

In order to increase heat conduction away from a plurality of rotor barsof a rotating machine, oil coolant is passed through the rotor bars. Oilcoolant is supplied to and removed from the rotor bars via left andright end plates. The end plates are preferably round disks located oneither end of the rotor. The end plates have conduits therein to allowthe flow of coolant oil in the rotor bars on one end and out on theother end. Holes located in a rotating hollow shaft under each end plateand communicating with the conduits of the end plates allow oil coolantto flow in and out of the hollow shaft. A restriction located near themiddle of the hollow shaft and between the end plates provides apressure differential to divert at least a portion of the coolant oil toflow through the rotor bars.

In summary, there is provided an improved rotating machine. The improvedrotating machine comprises: a rotating shaft: a plurality of conductiverotor bars spaced from the rotating shaft and fixed thereto through atleast one intermediate member, at least one of the plurality ofconductive rotor bars having at least one first internal conduit; andcirculation means for establishing a coolant circulation through thefirst internal conduit.

In a preferred implementation of the rotating machine, the rotatingshaft has a first wall defining a second internal conduit extending froman inlet end to an outlet end thereof. The rotating shaft further hasfirst and second coolant holes in the wall and communicating with thesecond internal conduit, wherein the coolant is circulated through thefirst internal conduit from the second internal conduit by way of thefirst and second coolant holes. Furthermore, each of the plurality ofconductive rotor bars have a first and second end where the at least onefirst internal conduit extends from the first to second end. A first endplate has a first bore in which the rotating shaft is sealingly fixed inproximity to the first coolant hole. The first end plate further hasmeans for sealingly fixing the first end of each conductive rotor barhaving the at least one first internal conduit thereto and a thirdinternal conduit for each of the plurality of conductive rotor barshaving the at least one first internal conduit for providingcommunication between the first coolant hole and the first end of thefirst internal conduit. A second end plate has a second bore in whichthe rotating shaft is sealingly fixed in proximity to the second coolinghole. The second end plate further has means for sealingly fixing thesecond end of each conductive rotor bar having the at least one firstinternal conduit thereto and a fourth internal conduit for each of theplurality of conductive rotor bars having the at least one firstinternal conduit for providing communication between the second coolanthole and the second end of the first internal conduit. Thus, thecirculation of coolant is established through the first, second, third,and fourth internal conduits for each conductive rotor bar having the atleast one second internal conduit.

The circulation means comprises either a full restriction plug disposedin the second internal conduit between the first and second coolantholes thereby diverting all of the fluid flow through the first, third,and fourth internal conduits for each conductive rotor bar having the atleast one first internal conduit. Alternatively, the circulation meanscomprises a partial restriction plug disposed in the second internalconduit between the first and second coolant holes. Thus, in thealternative version, which is also the preferred implementation, aportion of the fluid flow is diverted through the first, third, andfourth internal conduits for each conductive rotor bar having the atleast one first internal conduit and the remaining portion of the fluidflow continues through the second internal conduit of the rotatingshaft.

In yet another preferred implementation of the rotating machine of thepresent invention, each of the plurality of conductive rotor bars havethe at least one first internal conduit. In yet a more preferredimplementation of the rotating machine of the present invention, the atleast one first internal conduit comprises two first internal conduits,each extending from the first to second end of the conductive rotorbars.

In yet another preferred implementation of the rotating machine of thepresent invention, each of the first and second end plates further hasan access bore disposed in a fluid path of the third and fourth internalconduits, respectively, for facilitating the fabrication of the thirdand fourth internal conduits, and wherein the first and second endplates each further comprise a cover plate sealingly covering itsrespective access bore.

In yet still another preferred implementation of the rotating machine ofthe present invention, the rotating machine further comprises: acirculation conduit connecting the inlet end of the rotating shaft tothe outlet end of the rotating shaft; a pump disposed in a fluid path ofthe circulation conduit for establishing a fluid flow into the inletend, through the first, second, third, and fourth internal conduits foreach conductive rotor bar having the at least one first internalconduit, and out the outlet end; and a heat exchanger disposed in thefluid path of the circulation conduit for removing heat from the fluidflowing therein.

Also provided is a method for assembling the rotating machine of thepresent invention. The method comprises the steps of: assembling theplurality of conductive rotor bars to the at least one intermediatemember and the first end of each conductive rotor bar having the atleast one internal conduit to the first end plate; heating the topregion of a molten salts bath such that the top region is maintained ata normal brazing temperature; only immersing the first end plate and thefirst ends of the plurality of conductive rotor bars into the top regionof the molten salts bath; salts brazing the first end of each conductiverotor bar having the at least one internal conduit to the first endplate; either before or after the salts brazing of the first end of eachconductive rotor bar having the at least one internal conduit,assembling the second end plate to the second end of each rotor barhaving the at least one internal conduit to the second end plate; onlyimmersing the second end plate and the second ends of the plurality ofrotor bars into the top region of the molten salts bath; and saltsbrazing the second end of each conductive rotor bar having the at leastone internal conduit to the second end plate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus andmethods of the present invention will become better understood withregard to the following description, appended claims, and accompanyingdrawings where:

FIG. 1 illustrates a sectional view of the rotating machine of thepresent invention.

FIG. 2a illustrates a sectional view taken through line 2 a—2 a of FIG.1.

FIG. 2b illustrates a partial exploded view of the sectional view ofFIG. 2a.

FIG. 3a illustrates a sectional view of the rotor of the rotatingmachine of FIG. 1 taken through line 3—3 thereof.

FIG. 3b illustrates an enlarged sectional view of a rotor bar of FIG.3a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although this invention is applicable to numerous and various types ofrotating machines, it has been found particularly useful in theenvironment of electric motors and generators. Therefore, withoutlimiting the applicability of the invention to electric motors andgenerators, the invention will be described in such environment.

Referring now to FIG. 1, there is illustrated a sectional view throughthe end covers 102, bearings 104, and stator 106 of a rotating machineof the present invention, the rotating machine generally referred to byreference numeral 100 and depicted therein as an electric motor. Therotating machine 100 generally has a rotating shaft 108 rotatablysupported in the end covers 102 by the bearings 104. The rotating shaft108 rotates the rotor assembly 110 relative to the stator 106.

Referring now to FIGS. 2a and 2 b, there is illustrated the rotorassembly 110 of FIG. 1 in greater detail. The rotating shaft 108generally is hollow or tubular and thus has a wall 108 a defining asecond internal conduit 108 b extending from an inlet end 112 to anoutlet end 114 thereof. The second internal conduit 108 b is used tocarry cooling fluids, such as oil through the shaft to cool the shaft,and as will be described below, to also cool the conductive rotor bars.The fluid flow is shown as traveling in the direction from the inlet end112 to the outlet end 114, however, those skilled in the art willrecognize that the fluid flow can travel from end 114 to end 112 withoutdeparting from the spirit or scope of the present invention. Therotating shaft 108 further has first and second coolant holes 116, 118in the wall 108 a and communicating with the second internal conduit 108b.

Referring now to FIGS. 2a, 2 b, and 3 a in combination, a plurality ofconductive rotor bars 120 (hereinafter referred to as rotor bars) arespaced from the rotating shaft 108 and fixed thereto through at leastone intermediate member. The at least one intermediate member preferablycomprises a plurality of parallel stacked steel laminates 122. Eachsteel laminate typically has a central bore 122 a for acceptance of therotating shaft 108 therein and a slot 122 b corresponding to each of theplurality of rotor bars 120 for acceptance of each of the plurality ofrotor bars 120 therein. Each of the plurality of rotor bars 120 has afirst and second end 120 a, 120 b, respectively. At least one of theplurality of rotor bars 120 has a first internal conduit 124 extendingfrom the first to second end 120 a, 120 b of the rotor bar 120.

Referring now to FIG. 3b, preferably, each of the plurality of rotorbars 120 has the first internal conduit 124. More preferably, each ofthe rotor bars 120 has two first internal conduits 124, 126. The firstinternal conduits 124, 126 are preferably cylindrical (circular incross-section) for ease of fabrication. The rotor bars are preferablyteardrop-shaped as shown in FIG. 3b, having one end (closest to thestator 106) which is larger in cross-section than an opposite end. Atleast one of the first internal conduits is preferably located at thatpart of the rotor bar 120 which has the larger (or increased)cross-section. This concentrates the cooling fluid in the rotor bar atthe point where heat generated is the greatest and thus increases thecooling efficiency thereof.

Referring back to FIGS. 2a and 2 b, the rotor assembly 110 further hasfirst and second end plates 128 a, 128 b on either ends 120 a, 120 b ofthe rotor bars 120. The first end plate 128 a has a first bore 130 a foraccepting the rotating shaft 108. The first end plate is fixed andsealed to the rotating shaft 108 with the first end plate 128 a being inproximity to the first coolant hole 116. The first end plate 128 a issealed to the rotating shaft by means of first and second o-ring seals132 a, 134 a, disposed on either side of the first coolant hole 116 toprevent any fluid from flowing between the outer surface of the rotatingshaft 108 and the inner surface of the first bore 130 a. The first endplate 128 a can be fixed to the rotating shaft 108 in any manner knownin the art. Preferably, the first end plate 128 a is shrink fit to therotating shaft 108. Shrink fitting comprises heating the first end plate128 a so as to expand the diameter of the first bore 130 a and/or(preferably, and) cooling the rotating shaft 108 so as to decrease theouter diameter thereof. The first end plate 128 a is thereafterassembled in place on the rotating shaft 108 and the temperatures of thefirst end plate 128 a and/or the rotating shaft 108 are normalized(e.g., brought to room temperature) such that the first end plate 128 ais shrunk fit to the rotating shaft 108. The shrink fit also providesthe proper o-ring squeeze to provide a proper liquid seal between thefirst end plate 128 a and the rotating shaft 108.

The first end plate 128 a further has means for sealingly fixing thefirst end 120 a of each rotor bar 120, having the at least one firstinternal conduit 124, to the first end plate 128 a. The rotor bars 120are preferably located in position relative to the first end plate 128 aby insertion of their first end 120 a into corresponding counterbore 136a on the first end plate 128 a. The counterbore 136 a preferably has ashape and size substantially the same as the cross sectional shape andsize of the rotor bar 120 so as to also orient the rotor bars 120 intheir correct angular position.

The first end plate 128 a is preferably disc-like in shape and both thefirst end plate 128 a and the rotor bars 120 are fabricated fromaluminum. The means for sealingly fixing the first end 120 a of eachrotor bar 120 to the first end plate 128 a comprises a brazed joint atthe juncture between the first end plate 128 a and the first end 120 aof the rotors 120.

The first end plate further has a third internal conduit, referred togenerally by reference numeral 138 a. The third internal conduitprovides fluid communication between the first coolant hole 116 and thefirst end 120 a of the first internal conduit 124 (and alternativelyboth second conduits 124, 126) for all of the rotor bars 120 havingfirst internal conduit(s) 124 (126). The first end plate preferably hasa groove 140 a on the first bore 130 a in proximity to the first coolanthole 116 so that the first coolant hole 116 is in communication with thegroove 140 a and the groove 140 a is in communication with all of thethird internal conduits 138 a.

Preferably, the first end plate 128 a further has an access groove 142 adisposed in a fluid path of the third internal conduit 138 a. Becausethe first end plate 138 a is typically a thin plate, the access groove142 a facilitates easy fabrication of the third internal conduit 138 a.The access groove 142 a of the first end plate 128 a is then sealinglycovered with a cover plate 144 a. The cover plate 142 a is alsopreferably aluminum and brazed to the first end plate 128 a.

Referring to FIG. 2a, similarly, the second end plate 128 b has a secondbore 130 b for accepting the rotating shaft 108. The second end plate128 b is fixed and sealed to the rotating shaft 108 in the same manneras is the first end plate 128 a but with respect to the second coolanthole 118 and the second ends 120 b of the rotor bars 120. The second endplate 128 b is sealed to the rotating shaft 108 by means of third andfourth o-ring seals 132 b, 134 b, disposed on either side of the secondcoolant hole 118 to prevent any fluid from flowing between the outersurface of the rotating shaft 108 and the inner surface of the secondbore 130 b.

The second end plate 128 b further has means for sealingly fixing thesecond end 120 b of each rotor bar 120 having the at least one firstinternal conduit 124 to the second end plate 128 b. The rotor bars 120are also preferably located in position relative to the second end plate128 b by insertion of their second end 120 a into a correspondingcounterbore 136 b on the second end plate 128 b. The counterbore 136 bpreferably has a shape and size substantially the same as the crosssectional shape and size of the rotor bar 120 so as to also orient therotor bars 120 in their correct angular position.

The second end plate 128 b is preferably disc-like in shape and both thesecond end plate 128 b and the plurality of rotor bars 120 arepreferably fabricated from aluminum. The means for sealingly fixing thesecond end 120 b of each rotor bar 120 to the second end plate 128 balso comprises a brazed joint at the juncture between the second endplate 128 b and the second end 120 b of the rotors 120.

The second end plate 128 b further has a fourth internal conduit,referred to generally by reference numeral 138 b. The fourth internalconduit provides fluid communication between the second coolant hole 118and the second end 120 b of the first internal conduit 124 (andalternatively both first internal conduits 124, 126) for all of therotor bars 120 having first internal conduit(s) 124 (126). The secondend plate preferably has a groove 140 b on the second bore 130 b inproximity to the second coolant hole 118 which serves the same purposeas groove 140 a. Preferably, the second end plate 128 b, like the firstend plate 128 a, also has an access groove 142 b covered with a coverplate 144 b which is also preferably aluminum and brazed to the secondend plate 128 b.

It should be apparent to those skilled in the art, that two fluid pathsare established by way of the configuration of the rotating machine 100of the present invention. A first fluid path is established through thesecond internal conduit 108 b of the rotating shaft 108. A second fluidpath exists from the second internal conduit 108 b, through the thirdinternal conduit 138 a of the first end plate 128 a, through the firstinternal conduit(s) 124 (126) of the rotor bars 120, through the fourthinternal conduit 138 b of the second end plate 128 b, and finally backto the second internal conduit 108 b of the rotating shaft 108.

A circulation conduit 146 connects the inlet end 112 of the rotatingshaft 108 to the outlet end 114 of the rotating shaft 108 to enclose thetwo fluid paths allowing circulation of a coolant fluid. A pump 148 isdisposed in the fluid path of the circulation conduit 146 forestablishing and driving the fluid flow in the first and second fluidpaths. A heat exchanger 150 is disposed in the fluid path of thecirculation conduit 146 for removing heat from the coolant fluid flowingtherein.

A fluid flow means is used for establishing a circulating fluid flowthrough either both or one of the fluid paths previously described. Toachieve a fluid flow only in the second fluid path (i.e., through theend plates 128 a, 128 b, and rotors 120) a full restriction plug 152 isdisposed in the second internal conduit 108 a between the first andsecond coolant holes 116, 118 thereby diverting all of the fluid flowthrough the first, third, and fourth internal conduits 124 (126), 138 a,138 b for each rotor bar 120 having the first internal conduit 124,(126).

However, it is preferred that both the first and second fluid flows areestablished thereby cooling both the rotating shaft 108 and the rotorbars 120. Both fluid flows are preferably achieved with a partialrestriction plug 154 disposed in the second internal conduit 108 bbetween the first and second coolant holes 116, 118. The partialrestriction plug has an orifice 154 a which creates a pressuredeferential between the first and second coolant holes 116, 118 therebydiverting a portion of the fluid flow through the first, third, andfourth internal conduits 124 (126), 138 a, 138 b for each rotor bar 120having the first internal conduit 124, (126) and where the remainingportion of the fluid flow continues through the second internal conduit108 b of the rotating shaft 108. Although the restriction plug is shownwith the orifice 154 a, it is understood that the full restriction plug152 would not have an orifice. The pump 148 and heat exchanger 150 usedas well as any fittings and connections needed for connections to and ofthe conduits and rotating shaft are known in the art and theirdescriptions omitted for the sake of brevity.

The assembly of the rotating machine 100 will now be explained withreference to FIGS. 2a and 2 b. The at least one intermediate member 110(referred to in FIG. 1, and shown in FIGS. 2a and 2 b as laminations122) is assembled to the plurality of rotor bars 120 as described below.

The first end 120 a of each rotor bar 120 having the at least one firstinternal conduit 124 (126) is assembled into place on the first endplate 128 a, preferably by placement of the first end 120 a into acorresponding bore 136 a. Prior to or after assembly, all of the partsto be brazed are prepared for the brazing process, such as by cleaning,fluxing, etc.

The top region of a molten salts bath is heated such that the top regionis maintained at a normal brazing temperature. With the top region ofthe molten salts bath maintained at the proper brazing temperature, onlythe first end plate and the first ends of the plurality of rotor barsare immersed into the top region of the molten salts bath. The first end120 a of each rotor bar 120 having the at least one first internalconduit 124 (126) is then salts brazed to the first end plate 128 a.

After the salts brazing of the first end 120 a of each rotor bar 120having the at least one first internal conduit 124 (126), the second endplate 128 b is assembled to the second end 120 b of each rotor bar 120having the at least one first internal conduit 124 (126). Those skilledin the art would recognize that alternatively, both the first and secondend plates 128 a, 128 b, can be assembled before brazing of the firstend plate 128 a.

Similar to the first end plate 128 a, only the second end plate 128 band the second ends 120 b of the plurality of rotor bars 120 areimmersed into the top region of the molten salts bath. The second end120 b of each rotor bar 120 having the at least one first internalconduit 124 (126) is then salts brazed to the second end plate 128 b,thereby completing the assembly.

If each of the first and second end plates 128 a, 128 b is provided withan access groove 142 a, 142 b as discussed above, then the immersionsteps discussed above further include the immersion of a respectivecover plate 144 a, 144 b and wherein the salts brazing steps include thebrazing of the cover plates 144 a, 144 b to the respective end plates128 a, 128 b to sealingly cover the access grooves 142 a, 142 b therein.

Finally, the first and second end plates 128 a, 128 b are then assembledto the rotating shaft 108. As discussed above, the preferable method forassembling the first and second end plates 128 a, 128 b to the rotatingshaft 108 is by a shrink fit therebetween.

In summary, those skilled in the art would recognize that routingcoolant through the rotor bars of the rotating machine of the presentinvention puts the coolant in direct contact with the source of the heatthus improving thermal dissipation and improving the design andefficiency of the rotating machine. Thus, the materials andconfiguration of the present invention provides an efficient,structurally sound, and producible product.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for assembling a rotating machine, therotating machine comprising a plurality of conductive rotor bars spacedfrom a rotating shaft, each of the plurality of conductive rotor barshaving a first and second end, at least one of the plurality ofconductive rotor bars having at least one internal conduit extendingfrom its first to second end; a first end plate having a first bore inwhich the rotating shaft is sealingly fixed, the first end plate furtherhaving means for sealingly fixing the first end of each conductive rotorbar having the at least one internal conduit thereto, the first endplate having fluid flow means for providing fluid flow to the first endof the internal conduit; and a second end plate having a second bore inwhich the rotating shaft is sealingly fixed, the second end platefurther having means for sealingly fixing the second end of eachconductive rotor bar having the at least one internal conduit thereto,the second end plate further having fluid flow means providing fluidflow from the second end of the internal conduit, the method comprisingthe steps of: assembling the plurality of conductive rotor bars to theat least one intermediate member and the first end of each conductiverotor bar having the at least one internal conduit to the first endplate; heating the top region of a molten salts bath such that the topregion is maintained at a normal brazing temperature; only immersing thefirst end plate and the first ends of the plurality of conductive rotorbars into the top region of the molten salts bath; salts brazing thefirst end of each conductive rotor bar having the at least one internalconduit to the first end plate; either before or after the salts brazingof the first end of each conductive rotor bar having the at least oneinternal conduit, assembling the second end plate to the second end ofeach rotor bar having the at least one internal conduit to the secondend plate; only immersing the second end plate and the second ends ofthe plurality of rotor bars into the top region of the molten saltsbath; and salts brazing the second end of each conductive rotor barhaving the at least one internal conduit to the second end plate.
 2. Themethod of claim 1, wherein the fluid flow means of the first and secondend plates comprises a third and fourth internal conduit, respectively,wherein the method further comprising the steps of: providing each ofthe first and second end plates with an access groove disposed in afluid path of the third and fourth internal conduits, respectively, forfacilitating the fabrication of the third and fourth internal conduits;and sealingly covering each access groove with a cover plate.
 3. Themethod of claim 2, wherein the immersion steps further include theimmersion of a respective cover plate and wherein the salts brazingsteps include the brazing of the cover plates to the respective endplates to sealingly cover the access grooves therein.
 4. The method ofclaim 1, further comprising the step of assembling the first and secondend plates to the rotating shaft.
 5. The method of claim 4, wherein theassembling of the first and second end plates the rotating shaftcomprises the steps of: heating each of the first and second end platesso as to expand the diameter of the first and second bores therein;and/or cooling the rotating shaft so as to decrease the diameterthereof; and normalizing the temperatures of the first and second endplates and/or the rotating shaft such that the first and second endplates are shrink fit to the rotating shaft.